How many cycles will cost when using a multiplicaiton?

On a C2S35 you can do up to 35 18x18 single clock cycle multiplications in parallel.

See:

http://www.altera.com/products/devices/cyclone2/features/multipliers/cy2-multipliers.html

And at 50MHz it works like a charm and has enough slack to meet timing no matter what.

rbugalho I think * sign will infer a proper dedicated multiplier and not a logic based one (if the bit-widths allow it). How sure are you that it will not infer it ?